transcriptomics

In a print shop, every page of a book used to be set by hand. One mistake, and the whole print run is at risk. RNA sequencing of the brain looked much the same until recently: each sample demanded hours of manual work, and short reads, like torn scraps of pages, could not be pieced together into the full text of a gene. Now there is a production line that reads every page from start to finish.

In an orchestra that has been playing the same symphony for years, the musicians gradually start to drift: each one plays on their own, yet the notes remain the same. That is roughly what happens to cells as they age. Scientists have come up with a way to measure this discord, that is, how faithfully each cell follows the shared program of gene expression.

On a crowded train, some passengers ride in silence while others push toward the exit, shoving their neighbors aside. In every person's blood, mutant cells appear with age, and their fate is much the same: most changes are neutral, like passengers who are simply along for the ride, but some give a cell an edge, and it starts dividing faster than the rest.

At the end of every chromosome sits a cap made of repeating DNA letters: the telomere. For a long time it was measured as an average length across all chromosomes, as if judging a library by the average thickness of its books. But in humans, three ends, 17p, 20q, and 12p, are consistently shorter than the rest, and they are the ones more often linked to genome damage.